It is known to utilize agricultural implements comprising a plurality of frame sections, which are moveable relative to each other. Examples of such agricultural implements are cultivators and seed drills, which have two or more side sections that are retractable or extendable between a transport position and a working position.
In the working position, such agricultural implements often allow some relative movement between the frame sections, for example in order to compensate for unevenness of the ground being cultivated by the agricultural implement.
Retracting or extending the agricultural implement is often carried out using hydraulic cylinders. In connection with retracting or extending, it is desirable to keep a check on the position in which the frame sections are situated, for example in order to ensure that the retracting or extending is completed, that the retracting or extending does not exceed a limit value and/or that the agricultural implement does not risk overturning.
Measuring the relative positions of the frame sections using sensors that detect the position of one or more hydraulic cylinders is known from U.S. Pat. No. 6,220,366B1. Measuring the relative positions of the frame sections using measuring devices arranged near a joint between the frame sections is also known from U.S. Pat. No. 6,220,366B1.
Arranging sensors that detect the positions of the hydraulic cylinders is in itself a well-known and functioning technique but relatively expensive. Detecting the angular position of a joint is also in itself a well-known and functioning technique, but likewise expensive and besides more complex, since it generally requires modifications on both sides of the joint in order to determine the position of the latter. In addition, the environment in which the sensors are required to operate is fairly difficult, including vibrations, dust, dirt and moveable objects which may damage the sensors. Therefore, there is a need for a simpler and less expensive solution for monitoring the retraction/extension operation.